Oil compositions stabilized against oxidative deterioration



Patented June 15, 1954 STABILIZED AGAINST OIL COMPOSITIONS OXIDATIVE D ETERIORATION Oliver L. Harle, Berkeley, Calif., assignor to California Research Corporation, San Francisco, Calif., a corporation of Delaware No Drawing. Application March 1, 1952, Serial No. 274,518

Claims.

The present invention relates to the stabilization of oils against oxidative deterioration. More particularly, the invention has to do with the preparation of an oleaginous composition comprising a major amount of a normally oxidizable oil and a minor amount each of a hydroxy aromatic compound and of a thiocarbonic acid derivative, each being selected from specific classes of compounds. In accordance with the invention, it has been found that the combination of the aforesaid thiocarbonic acid derivative and hydroxy aromatic compound has a synergistic anti-oxidant effect.

Among the adverse effects caused by oxidation may be mentioned the formation of corrosive acidic products, sludges, varnishes, resins and other oil-insoluble products, as for example, with mineral oils. Other oils, such as certain synthetic hydrocarbons, tend to further polymerize on oxidation, thus becoming undesirably viscous, while other synthetic oils, for example the polyalkylene glycol type, tend to depolymerize giving 01f volatile products. Other oils thicken and become rancid, for example the animal and vegetable fatty oils.

Now I have found that I can substantially increase the resistance to oxidation of these oils and others, whereby their quality and nature are maintained unimpaired over a long period of time either during use or in storage, by the incorporation in the oil of a small amount of a hydroxy aromatic compound in addition to a small amount of a non-acidic thiocarbonic acid derivative selected from the class consisting of esters, amides, salts, acyl disulfides and thioanhydrides of thiocarbonic acids.

More specifically, the non-acidic thiocarbonic acid derivative is one which is soluble in the oil to the extent of at least about 0.05%, preferably about 0.1%, by weight of the finished oil, and which has a molecular weight of at least about 150.

In general, the aforesaid thiocarbonic acid derivative may be represented by the following formulas:

or arylalkyl radicals.

Specific examples of thiocarbonie acid derivatives contemplated by the invention are zinc din-butyldithiocarbamate, zinc i-propylxanthate, zinc sec-amyltrithiocarbonate, zinc phenyl-nbutyl dithiocarbamate, butyl di-n-butyl dithiocarbamate, tolyl di-n-butyldithiocarbamate, dibenzyltrithiocarbonate, di-i-butylxanthate, zinc salt of dithiocarbonic acid morpholide, tetramethyl thiouramdisulfide, di-i-propyl xanthogen, and sec-butylxanthic thioanhydride.

In general, the amount of thiocarbonic acid derivative required for substantial inhibition of the base oil against oxidation ranges from about 0.03% to about 10% by weight of the finished oil, a satisfactory working amount residing within about the range of 0.1 to 1.0%, with an optimum of about 0.2% by weight of the finished oil.

The hydroxyaromatic compound contemplated by the invention is one which has a minimum solubility in the base oil of about 0.05 per cent by weight of said oil, and preferably about 0.5 per cent. Moreover, the hydroxy-aromatic compound is one which has at least a total of ten carbon atoms in the molecule. These compounds are ring-substituted phenols, ring-substituted or unsubstituted naphthols, anthrols and the like.

The substituent group can be hydroxy, amino, mercapto, alkoxy, aryloxy, thio, alkyl, aryl, alkaryl and arylalkyl radicals. However, substituent groups containing oxygen which are acidic or acid strengthening in nature, such as nitro, carboxyl and sulfcnic acid radicals, which are not further oxidizable are less desirable and for practical purposes are avoided.

Preferred classes of hydroxyaromatic compounds are naphthols and phenols, the latter being substituted on the para position with a hydrocarbon group, such as an alkyl group; and phenols having a second free hydroxyl group (dihydric phenol) or amino group (amino phenol) on either the orthoor para-position to give an orthoor para-dihydroxy benzene or an orthoor para-aminohydroxy benzene.

Specific examples of hydroxy aromatic compounds falling within the purview of the invention are t-butylhydroquinone, di-t-butyl resorcino1, t-butylcatechol, 1,2dihydroxynaphtha1ene, 1,4 dihydroxynaphthalene, 1,2 dihydroxy-4= phenyl benzene, 5-octy1-l-hydroxynaphthalene, 1,3 dihydroxy-5-cetoxybenzene, 1,2-dihydroxythianthrene, l-hydroxy-d-amino naphthalene,1- hydroxyl-isooctylamino benzene, fi-naphthol, a-naphthol, di-B-naphthol, i-t-butyl2-phenylphenol, 2,2-di(p-hydroxyphenyl) propane, 1-

amino-3-pentadecylphenol, and 2,6-dit-butyl p- 7 cresol.

In general, the amounts of hydroxy aromatic compound employed in accordance with the invention reside within about the range of 0.05% to 5.0% by weight of the finished oil, and preferably 0.1% to 2.0%, by weight of the finished oil.

Examples of commercially available base oils which may be benefited by the practice of the present invention are highly refined mineral ."ny-

drccarbon'lubricating oils, which because of the exhaustive refining thereof contain'substantially no aliphatic sulfur materials, for examplmwhite oil. Other base oils are synthetic hydrocarbon oils or olefin polymer oils, for example the polybutenes and others derived from the lower olefins, such as-ethylene, the propylenes, pentenes, etc, and from the Fischer-Tropsch process. Additional examples of base oils are the polyalkylene glycols of lubricating oil viscosity derived most advantageously from 1,2-propylene oxide, these oils, preferably having the terminal hydroxyl groups esteriiled and/or etherified. Also advantageously treated in accordance with the invention are the diester oils, that is, those derived .from the esterification of certain dicarboxylic acids, for example adipic and sebacic, with alcohols, for example butyl hexyl, and octyl alcohols. Another important class of synthetic base oils are those containing silicon, for example the Anti oxidant ance to oxidation possessed by the compositions prepared in accordance with the invention is the use of the apparatus and procedure described in Industrial and Engineering Chemistry, vol. 28,

p. 26 (1936), wherein the rate of oxygen absorption at constant pressure by adefinite weight of oil is regarded as a measure of the oxidative stability of the oil. According to this procedure, the oil sample is placed in an absorption cell, provided in the bottom with a fine-fritted glass filter to disperse-the oxygen stream, circulating through the system at a constant rate, into fine bubbles. In'obtaining the data hereinbelow appearing, thefollowing modified apparatus and procedure were employed.

The oxidation or absorption cell is constructed of a large glass tube with the head portion having a connection for introducing oxygen, an annularspace surrounding the upper end of the tube and a fitting for a removable high speed glass stirrer. The annular space contains potassium hydroxide. pellets for the removal'oi water, carbon dioxide, volatile 'aldehydes, etc. The lower portion of the cell which contains thesample to be tested is immersed in an'oil bathat a temperature of about-340 F: During the test,"the oil sample is rapidly agitated bymeansof a high speed stirrer and is-kept' under a pressure of about 1 atmosphereofpure oxygen, the volume of oxygen added being automatically ITE- corded. 'The time 'in hoursrequired ior "100 gramsof oil toabsorb 1200 cc. of oxygen isc'alled the Induction Period (I. 1 and represents the point at which-the sample begins to. absorb oxygen or oxidize. r

Thefollowing tabulated data were obtained from a number of experiments performed in accordance with the test above described.

In Table I,- the base oil employed was a medicinal white oil having a viscosity of'about :350 SSU at 100 F. It was prepared from a suitable distillate fraction of a California naphthenic type'crude byrphenol treatment followed by exhaustive treatment with fuming sulfuric acid. and

finished by percolating through fullers earth.

' TABLE I efiect'oj hydroacyaromatic compound and thiocarbonic acid derivative on white oil InducticnPeriod, Hrs. at 340 F.

Percent Tnocar- E3932? Wth r 1 Wit11)101ltThidO-- gvith ugaz onic 1 on iocarcar onic aci i(py roxy- ThlOCBIbOlllC Acid Deuvative Acld' (pplggro iiv bani, Acid Derivative; but phenyl) Derivative Propgne, -'derivative and with 2,2-di- Propanabut 2,2-di(p-hydroxy- (p-hydroxywith Thicphenyl) Propane phenyl) carbonic Acid Propane Derivative 1. Zinc dim-butyl dithiocarbamate 0.1 0.1 29 1.0 7. 2. Zinc i-propylxanthate 0.1 0.1 '21 1.0 1. 3. 'lctramethyl thiouramdisu1fide 0.1 0.1 24 1.0 0. 4. Di-sec.-huty1xanthogen 0.1 0.1 23 1.0 0. 5. Butyl di-n-butyldithiccarbamate 0.1 0.1 20 1.0 0. 6. Di-i-propylxanthlc thioanhydrida 0.1 0.1 14 1.0 0. 7. Zinc t-butyltrithiocarbonate 0.1 0.1 31 1.0 2.

orthosilicates, preferably those-in which 'the'alkyl groups attached to oxygen bound to siliconcontain at least three 1 carbon atoms in branched chain structure, for example bis (2-butyl).bis(2- ethyl-l-butyl) silicate, and isopropyl-tris(2*--pentyl)si1icate; and the polysiloxanes suchas-hexa- (Z-ethyl-l-butoxy) disiloxane.

A convenient method ofmeasuring the resist;-

It will be observed from these data that the combined inhibiting effect of each of the thiccarbonic acid derivatives and the aromatic amine is far greater than'the'sum of the effects of the individual additives used separately.

In Table II, the polypropylene glycol oil was an ethylhexanol-initiated'propene oxide polymer 7 of molecular weight about900.

TABLE 11 Anti-oxidant efiect of aromatic amine and thincarbonic acid derivatives on polypropyleneglycol oil Induction Period, Hrs. at 340 F.

Percent Percent Thio- -d (p- Thiocarbonic Acid Derivative carbonic Acid hydroxyggg gggg 852?: 5 3 2 53? Denvative ghenyl) rivative and 2,2- rivative, but with phenyl) Propane phenyl) Propane NE E 1. Di-i-propyl xanthogen 2.1 0. 5 3.5 0.1 2. Tetrainethylthiouramdisulfide. 1.7 0.6 4.0 0.1

3. Di-n-butyldithiocarbamate-initiated propene oxide polymer (M01. Wt. about 500) l0 0. 5 4. 0 0.1 4. Butylxanthate-initiated propene oxide polymer (M01. Wt. about 500) 0.5 3.0 0.1

. Table III is intended to illustrate the antitypes defined on a representative number of base oxidant effect on the same base oil as employed oils.

TABLE IV Induction Period, Hrs. at 340 F.

Except as indi- Base Oil cated,with0.1% Except as indl- Except as indip-tert -B utyl cated, only 0.1% cated, only 0.1% Oatechol and ptert.-Butyl Di-aec.-butyl- 0 1 D ls e c Oatechol xantliogen butylxanthogen M a M Polybutene polymer-M. W., about 3.6 (0.2% p-t-butyl 0.0 (0.2% p-t-butyl 0.0 (0.2% Di-sec.- 400. catechol; 0.2% catecho butyl-xantho- Di-sec-butylgen). xanthogen). Bis(2-ethylhexyl) sebacate. 32.0 3.2 1.2. Tetra-(2ethylbutyl) silicate 5.4 0.8 0.0. Tricresyl phosphate 12.0 2.8 1.4. Polypropylene glycol 1 3.7 (0.5% putyl 0.0 (0.5% p-t-butyl 0.0 (1.7% Di-sec.- eatechol; 1.7% catecho butyl-xanth o- Di-see.butylgen). xanthogen). Polypropylene glycol by vol- 2.9 0 1 0.0.

ume, mineral white 01]. Hexa-sec. butyldisiloxane 6.0 0 4 0.3.

l Eth lhexanol-initiated propene oxide polymer, Moi. Wt. about 900. 1 Po ypropyleneglycol"=isooctanol-initiated propene oxide polymer acetate, Mol. Wt. about 600'. "Mineral white oil=at0cl: prepared as previously described (Page 6), but with viscosity of about 72 Sen at F. in Table I by a representative number of hy- Obviously, many modifications and variations droxyaromatic compounds and tetramethyl-thioof the invention as hereinbefore set forth may be uramdisulfide. made without departing from the spirit and scope TABLE III Anti-oxidant e17ect of various hydroxyaromatic compounds and a thiocarboaiic acid derivative on white oil Induction Period, Hrs. at 340 F. Percent Percent Tetra Without Tetra- Without H Hydroxyaromatic Compound ';%i g& methylthiogfiggg fggfi ggg methylthiouramdroxyaromatic pound urlgrfriidiand HydroXyam ditshullfiidei, but Cornglol ncti, but

a e W1 y roxy- W1 e ramane Compound aromatic Cornmethylthlopound uramidisulflde 1. 2,6-Di-t-butyl- -cresol 0.1 0.1 6.5 2.1 0.9 2. p-t-Butylcatec o1 0.1 0.1 7.3 1.5 0.9 3. 4-t-Butyl-2-phenylphenol 0.1 0.1 3.4 0.6 0.9 4. 2,2-Di(p-hydroxyphenyll propane 0. 1 0. 1 21. 0 1. 0 0. 9 5. Z-Pentadecylhydroquinone 0.1 0.1 21.0 2.3 0.9 6. 4-Amino-E-pentadecylphenol 0.1 0.1 31.0 3.2 0.9 7. a-Naphtho 0.1 0. 1 12.9 4.1 0.9 8. fl-Naphthol- 0.1 0.1 7.2 1.0 0.9 9. Di-fi-Naphth 0.1 0.1 5.1 0.2 0.9

The data accumulated in Table IV illustrates thereof, and therefore only such limitations the anti-oxidant effect of hydroxyaromatic comshould be imposed as are indicated in the appounds and thiocarbonic acid derivatives of the pended claims.

I claim:

1. An oil composition having improved stability toward oxidation consisting in major portion of a normally oxidizable oil, together with from about 0.1 to 1% by weight of a sulfur-containing compound selected from thegroupponsisting of tetramethyl thiouramdisulfide and di secL-butylxanthogen and about 0.1 to 2% by weight of a hydroxy-substituted aromatic hydrocarbon selected from the group consisting of 2,2'di(p-hydroxyphenyl) propane and p-tert.-butylcatechol.

2. An oil composition having improved stability toward oxidation consisting in major portion of a normally oxidizable oil, together with from about 0.1 to 1% by weight oi? di-sec.-butylxanthogen and about 0.1 to 2% byweight of 2,2-.di(phydroxyphenyl) propane.

V 3. An oil composition having improved stability toward oxidationconsisting in major portion of a normally oxidizable oil, together with from about 0.1 to 1% uramdisulfide and about 0.1 .to. 2% byweight of 2,2'-di(p-hydroxyphenyl) propane.

by weight of tetramethyl thio 4. An oil composition having improved stability toward oxidation consisting in major portion of a normally oxidizable oil,- together with from about 0.1-to 1% byweight oftetramethyl thiouramdisulfide and about 0.1-to 2% by weight of p-tert.-butylcatechol.

' 5. An oil composition having improved stability "toward oxidation consisting in major portion of a normally oxidizable oil, together with from about 0.1 to 1 by weight of di-sec.butylxanthogen and about 0.1 to 2% by weight of p-tert.- butylcatechol.

-: References Cited in'the file of this patent UNITED STATES PATENTS Number Name Date 2,335,017 McNab et a1 'Nov.'23, 1943 2,394,530 Denison'et 'al ;Feb. 12, 1946 2,400,106 Denison et al May 14, 1946 2,440,530 7 Yates Apr; 27, 1948 2,580,274 Bergstrom et a1 Dec. 25, 1951 

1. AN OIL COMPOSITION HAVING IMPROVED STABILITY TOWARD OXIDATION CONSISTING IN MAJOR PORTION OF A NORMALLY OXIDIZABLE OIL, TOGETHER WITH FROM ABOUT 0.1 TO 1% BY WEIGHT OF A SULFUR-CONTAINING COMPOUND SELECTED FROM THE GROUP CONSISTING OF TETRAMETHYL THIOURAMDISULFIDE AND DI-SEC.-BUTYLXANTHOGEN AND ABOUT 0.1 TO 2% BY WEIGHT OF A HYDROXY-SUBSTITUTED AROMATIC HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF 2,2'' -DI(P-HYDROXYPHENYL) PROPANE AND P-TERT-BUTYLCATECHOL. 